Production of aromatic hydrocarbons from six carbon aliphatic diols



United States PatentO PRODUCTION OF AROMATIC HYDROCARBONS FROM SIXCARBON ALIPHATIC DIOLS Arthur William Charles Taylor, David Gwyn Jones,and

Morag Lauchlan Noble, Nortou-on-Tees, England, assignors to ImperialChemical Industries Limited, a corporation of Great Britain No Drawing.Application December 27, 1951, Serial No. 263,683

Claims priority, application Great Britain January 17, 1951 4 Claims..(Cl. 260-668) This invention relates to the production of aromatichydrocarbons. i e

According to the present invention, there is provided a process for theproduction of'aromatie hydrocarbons, which comprises the step ofcontacting a diol having a chain of at least six carbon atoms at atemperature within the range of 300 to 750 C. and in the vapour phasewith a catalyst as hereinafter defined.

Diols suitable for use in the processor thepresent invention include,for example, hexane-dials and hexenediols, which give rise to benzene ontreatment according to the process. Similarly hexane-diols andh'exene-diols containing a methyl substituent in the carbon chain giverise to toluene. However, the most important embodiment of the inventionresides in the production of aromatic hydrocarbons from diols having astructure:

CCH=CH-C /$H 4 o-cH.om J R, n n R.

or mixtures thereof, in which R1, R2, R2 and R4 are selected fromhydrogen, methyl, ethyl, n-propyl and isopropyl, the said diols havingat least eight carbon atoms. Thus, a xylene hydrocarbon fraction rich inpara-xylene may be produced from 2,5-dimethylhex-3 ene-2,5-diol, and/ or2,5-dimethylhexane-2,S-diol.

Catalysts suitable for use in the process of the present invention arethose normally employed in aromatisation reactions. Those comprisingmetals, of group VIII of the periodic system, and the oxides ofchromium, molyb-' denum and vanadium are particularly-suitable.Thelatter may conveniently be employed in conjunction with othermetallic oxides, such as alumina and magnesia. It is particularlypreferred to employ a supported platinum catalyst, such as platinum oncharcoal, or a chromic oxide-alumina catalyst.

A chromic oxide-alumina catalyst may be produced by dehydrating aluminatrihydrate, AI2O3.3H2O, at a temperature of 400 C. until the productcontains from 9 to 11% by weight of water. The product is pelleted usinga suitable pelleting lubricant, subsequently heated if necessary at atemperature of 700 C. to remove this lubricant if its presence isundesirable, and the pellets are then soaked in a solution of chromicacid until they acquire the desired chromium content. They are thendried at an elevated temperature of, for example, 400 C. The chromiumoxides content of the final catalyst is preferably to 15% by weight. Itis also advantageous to incorporate a minor amount of magnesium chromateinto the catalyst; a suitable amount is 2% by weight, expressed as thepercentage by weight of MgO in the final catalyst.

2,737,534 Patented Mar. 6, 1956 The conversion of the diol to aromatichydrocarbons is preferably carried out as a continuous process. Thetemperature at which the conversion is carried out should be within therange of 300 to 750 C., but the optimum temperature depends upon thediol to be converted and the catalyst employed. Thus, when using achromic oxide-alumina catalyst, a suitable temperature is one lyingwithin the range of 500 to 550 C.

The process of the present invention may be carrie out by passing thediol to a vaporiser prior to introducing it into the converter. The dialmay be" introduced 1 inot the vaporiser in the solid orliquid form, or,alternatively, it may be introduced into the reactor or vaporiser in theform of a solution, in, for example, water or methanol. I

The process may be carried out in the presence of a carrier gas such ashydrogen or nitrogen which may may be produced by any convenientprocess.

be mixed with the vaporised diol, and the mixture passed through thecatalyst bed maintained at the desired -temperature.

The diol for use in the process of the present invention For example,when 2,5-dimethylhex-3 ene-2,5-diol is employed, this may be produced bycondensing acetone with acetylene in the presence of potassiumhydroxide, or a potassium alkoxide, and subsequently subjecting the2,5-di- 1 methy1hex-3 yne-2,5-diol produced to partial hydrogenaouscaustic alkali of the aluminium from a finely divided iron-aluminiumalloy containing, for example, 50% by weight of iron. The hydrogenationmay be carried out by dissolving the acetylenic diol in a suitablesolvent, for example, methanol, ethanol or ethyl acetate, and contactingthis solution with hydrogen, in the presence of the selected catalyst.This hydrogenation may be carried out at room temperature andatmospheric or superatmospheric pressure.

If 2,5-dimethylhexane-2,5-diol is to be employed as the startingmaterial, this may be produced by the hydrogenation of 2,5-dimethylhex-3yne-2,5-diol, prepared as hereinbefore described, using a hydrogenationcatalyst. For example, platinum, nickel and copper catalysts may beemployed. The platinum may be used ina finely-divided form, for example,as platinum black, or it may be supported on an inert carrier, forexample, kieselguhr.

The nickel and copper catalysts for the hydrogenation prepared, forexample, by the substantially complete exwith alkali of aluminium orsilicon from an alloy contain traction-of aluminium from anickel-aluminium or copperaluminium alloy by means of a solution ofalkali. Fo-

raminate catalysts are also suitable for use in the process. These maybe prepared by the partial extraction ing one of these elements andnickel or copper. Suitable alloys are copper-aluminium alloys,containing 40 to by weight of copper, nickel-aluminium alloys containing30 to 65% by weight of nickel; copper-silicon alloys containing 80 to92% by weight of copper.

The optimum conditions for the hydrogenation depend upon the catalystemployed. With a platinum catalyst, the process may be carried out atatmospheric pressure and temperature, but when using Raney nickel, it ispreferred to operate at elevated temperature and pressure.

It is an important feature of the present invention that a mixture of2,5-dimethylhex-3 ene-2,5-diol and 2,5-dimethylhexane-2,5-diol may beemployed in the aromatisation reaction. Thus, the product obtained byhydrogenating 2,5-dimethylhex-3 yne-2,5-diol, such that between-1 and 2moles of hydrogen are absorbed per mole of yne-diol may be passed to thearomatisation step without separating the saturated and unsaturateddiols from each other.

It should also be noted that when 2,5-dimethylhex-3 ene- 2,5-diol isconverted to Xylenes by the process of the present invention,2,5-dimethylhexane-2,5-diol may be produced in the conversion zone as anintermediate product, particularly when added hydrogen is also present.Thus, the present invention is intended to cover themode of operation inwhich, in the same conversion zone, 2,5- dimethylhex-3 ene-2,-5-diol isinitially converted wholly or partially to 2,5-dimethylhexane-2,5-diol,and this mixture is then aromatised to xylene hydrocarbons, and, inparticular, to para-xylene.

In the process of the present invention, aliphatic hydrocarbons areproduced as by-products. Thus, when the starting material is2,5-dimethylhex-3 ene-2,5-diol and/or 2,5-dimethylhexane-2,5-diol,aliphatic hydrocarbons such as dimethallyl,1,l,4,4-tetramethylbutadiene, and dimethylhexenes may be produced asby-products. These are preferably recycled to the conversion zone to--gether with a further charge of diol.

Example 1 231 grams of 2,5-dimethylhex-3-yne-2,5-diol were dissolved inmethanol. 50 grams of a Raney nickel catalyst were added, and thehydrogenation of the diol carried out at 50 C. and 25 atmospherespressure. When hy drogen absorption had ceased, the product wasfiltered, and the methanol removed. The product, 2,5-dimethy1-.hexane-2,5-diol was a white crystalline solid, melting at 84 C. Theproduct weighed 197.3 grams, correspond: ing toa yield of 83 100 gramsof 2,5-dimethylhexane-2,5-diol were dissolved in 250 mls. of methanol.The solution was passed at a rate of 62 mls./ hour over 250 mls. of achromic oxide on alumina catalyst containing on analysis 13% by weightof oxides of chromium, 2% by weight of m ag-. nesia (present asmagnesium chromate) and 85% by weight of activated alumina. Hydrogen wasalso passed over the catalyst at a rate of litres/hour. This catalystwas maintained at a temperature of 500 C. i i

The reaction product contained 43.7 grams of liquid, of which 9.5 gramswere water, and 34.2 grams were a water-insoluble product. Since in acontrol experiment it had been established that under these conditionsmethanol itself gives rise to no. liquid products, the 34.2 grams ofwater-insoluble product were derived from the diol.

On distillation, the water-insoluble product gave frac-. tions,-which oninfra-red analysis showed that lowing compounds had been formed:

Dirnethylhexanes 3.6

the fol- 4 Hence 15.1 grams of aromatic hydrocarbon were identilied, andof this amount, 98.4% by weight was p-xylene. This corresponds to a passyield of p-xylene of 20.5%.

Furthermore, 15.5 grams of dimethylhexane, dimethallyl andtctramethylbutadiene were obtained, as shown in the table above, andthese-compounds may be readily aromatised in high yield to paraxylene.

Example 2 1 were isolated. On distillation and infra-red analysis, thiswas found to contain 11.8 grams of para-xylene, which corresponds to ayield of 36% We claim: I, 1. A process for the production of hydrocarbonmixtures'containing p-xylene which comprises the step of contacting'atleast one dihydric alcohol selected from the group consisting of2,5-dimethy1hex-3 ene-2,5-diol and 2,5-dimethylhexane-2,5-diol in thepresence of hydrogen at a temperature within the range of 300 to 750 C.in the vapor phase with a catalyst consisting essentially of ,chromicoxide and alumina.

by weight;

3. 'A 'process as recited in claim 1 in which a temperature within therange of 500 to 550 C. is employed.

4. A process as recited in claim '1 in which said cata lyst contains aminor amount of magnesium chromate.

References Cited in the file of this patent UNITED STATES PATENTS2,157,365 Vaughn May 9, 1939 2,250,445 Bruson et al. July 29, 19412,302,345 Pesta et al. Nov. 17, 1942 2,419,030 Otto Apr. 15, 19472,569,441 Al'quist et al. Oct. 2, 1951 1 OTH REFERENCES Komarewsky-et'al.: Jour. Amer. Chem. Soc., vol. 61 (1939), pages 2525-2527 (3 pages).

Johnson et al.: Industrial and Eng. Chem, vol. 38, pages 990 996(October 1946; 7-pages).

Plate-ct al.: Chem. Abstracts, vol. 42 (1948), col.

1 7234c, abstract'from Doklady Akad Nauk, USSR, vol.

59 (l948), pages 1305-8.

Kyriakides Apr. 21, 1914

1. A PROCESS FOR THE PRODUCTION OF HYDROCARBON MIXTURE CONTAININGP-XYLENE WHICH COMPRISES THE STEP OF CONTACTING AT LEAST ONE DIHYDRICALCOHOL SELECTED FROM THE GROUP CONSISTING OF 2,5-DIMETHYLHEX-3ENE-2,5-DIOL AND 2,5-DIMETHYLHEXANE-2,5-DIOL IN THE PRECENCE OF HYDROGENAT A TEMPERATURE WITHIN THE RANGE OF 300* TO 750* C. IN THE VAPOR PHASEWITH A CATALYST CONSISTING ESSENTIALLY OF CHROMIC OXIDE AND ALUMINA.